SAN FRANCISCO — The America’s Cup that promised thrills and excitement, a veritable “NASCAR on the water,” pushing sailors and their boats to their limits, turned deadly Thursday when Sweden’s Artemis Racing capsized its 72-foot catamaran during a training day on the bay, claiming the life of a British Olympian who became trapped underneath.

Andrew “Bart” Simpson, 36, who won gold in 2008 and silver in 2012 for Great Britain, was submerged for 10 minutes, authorities say, and efforts to revive him on the water and on the dock of the St. Francis Yacht Club were unsuccessful. Chatter heard on a sailing radio channel suggested crew members couldn’t find him at first.

“The entire Artemis Racing team is devastated by what happened,” Artemis CEO Paul Cayard said in a statement. “Our heartfelt condolences are with Andrew’s wife and family.”

Cayard declined to discuss what might have caused the capsize near the Ferry Building, between the Golden Gate and Bay bridges, at about 1 p.m. Wind was blowing at about 20 mph, normal conditions for this time of year and speeds that are expected to be similar when the regatta begins July 5.

Thursday’s tragedy follows a highly-publicized capsize of Team USA Oracle’s boat last fall and comes just two months before the Bay Area hosts the world’s most famous sailing race. In the October capsize, the Oracle boat was severely damaged, its mast broken and hulls punctured as strong currents dragged it through choppy waters under the Golden Gate Bridge. But unlike Thursday’s wreck, no one was injured in the October incident.

Oracle immediately reviewed its safety policies and required sailors, along with wearing life jackets and crash helmets, to carry knives and small oxygen canisters in case they get trapped under the trampoline net that connects the two pontoons. It wasn’t clear Thursday whether Artemis sailors had the same safety equipment.

All the teams’ crews, considered the best sailors in the world, were clearly aware of the dangers of manning boats that can reach speeds faster than 40 mph. Artemis helmsman Loick Peyron, in an interview after Oracle capsized, said that of all the boats he has sailed, the AC72 “is the trickiest.”

“It’s a bit like putting a V8 or V12 on a go-cart. So it is no easy matter making use of all that power. We saw what can happen when Oracle capsized,” he said in November. “These machines require caution. … I’m here to find just how far we can take things and avoid those hairy moments, when the boat starts to dig in, for example.”

Quick studies of aerial photos of the capsized Artemis boat suggest it may have done just that: pitch-poled end-over-end when the bow at the front of the boat “dug in” to the water, just like Oracle did last fall.

“It looks as though the port-side hull twisted badly or broke in half and looks as though the forward cross beam — a major structural beam that holds the front and back together — apparently broke or parted from the port-side hull,” said Andy Turpin, managing editor of Mill Valley’s Latitude 38 sailing magazine, after reviewing the photos. “When one bow buries into the water, then all the forces of inertia push the boat over head first.”

A story in Wired.com suggested, however that the capsize was not caused by sailors pushing the boat too hard, but by the boat itself breaking apart because of either faulty engineering or construction.

Turpin added that he was struck by how mangled the boat appeared. When Oracle capsized, the damage occurred not so much because of the capsize itself, but when the mast rammed the hulls that drifted for hours in the choppy water. Thursday’s conditions were much milder, and it was “initially surprising when you zoom in and see how much damage was done to the hulls and crossbeams.”

It isn’t clear how the sailors fell from the boat or whether Simpson might have been knocked out before hitting the water. Chase boats from Oracle Team USA, as well as the New Zealand and Italian teams that only recently moved to San Francisco to prepare for the regatta, rushed to the scene.

When Artemis crew members were finally able to pull Simpson from the water, they detected no pulse or breath. CPR was started afloat then continued for 20 minutes on the dock of the St. Francis Yacht Club before he was pronounced dead at 1:43 p.m.

A second crew member was taken to the yacht club and treated for lacerations. The other nine crew members were not injured.

Simpson’s death appears to be the second during an America’s Cup campaign. In February 1999, the Spanish team lost crewman Martin Wizner, one of the country’s leading sailors, during training when he was hit in the head after the block of a halyard broke.

“It’s a tragic day,” San Francisco Fire Chief Joanne Hayes-White said Thursday. “This is someone that is well-known and well-regarded as an expert racer.

How the tragedy will affect the Artemis team and plans for the America’s Cup this summer is also uncertain. During a news conference Thursday afternoon at the Artemis base in Alameda, Cayard said his crew and their families were his biggest concern.

“It’s a shocking experience to go through, and we have a lot to deal with in the next few days in terms of ensuring everybody’s well-being,” said Cayard, a San Francisco native. “We’re focused on the people. That’s what we’re working with and on, and we’ll give you more information when we’re able to.”

San Francisco police spokesman Albie Esparza said the department’s major accident investigations team will lead the inquiry into the crash. The same team investigated an accident that killed five people during a yacht race off the Farallon Islands in April 2012.

“They’re going to be tasked with finding out exactly what happened, talking to any witnesses and reconstructing the accident as best we can,” Esparza said.

Turpin, from the sailing magazine, said that the fact that two America’s Cup teams have suffered catastrophic capsizes doesn’t bode well for the summer of sailing.

“It does give one pause if the boats break up this easily,” Turpin said. “This is only the second flip in the AC72, and both of them broke in one way or another.”

Turpin surmised that Artemis “took every caution,” and it’s too soon to tell what factors contributed to the capsize.

“I’m not in a position to condemn these boats as too fast or too edgy,” he said. “But certainly there’s a great temptation to push speed and push the design parameters to the limits so they can go as fast as possible. The faster they go, of course, there are dangers.”

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